This invention relates to signal receiving apparatus of the type which is capable of receiving broadcasted radio signals and which is provided with a storage device for storing preset channel identity signals representing particular channels to which the apparatus is tuned and, more particularly, to such apparatus which additionally is provided with a memory device for storing preset control signals which are associated with the particular channels identified by the stored, preset channel identity signals, which control signals are used to establish desired operating conditions of the signal receiving apparatus for each such channel.
In typical radio receiving apparatus, such as the type which is adapted to receive FM and/or AM signals, a tuning section is provided wherein a variable frequency local oscillating signal is mixed with an incoming radio signal to produce an intermediate frequency (IF) signal from which the received, broadcasted information is demodulated. Heretofore, the frequency of the local oscillating signal is varied by varying one or more reactive elements, such as an air capacitor, which is included in the local oscillator circuitry. In an improvement over this apparatus, the usual mechanically-operable air capacitor has been replaced by a voltage-controlled reactance device, such as a voltage-controlled capacitor, known as a varicap diode. By avoiding the use of mechanical elements in the tuning section, it is possible to employ digital techniques for controlling the voltage-controlled capacitor and, thus, to select a desired tuning condition for the signal receiving apparatus.
A tuning section which relies on digital techniques, as aforesaid, may include a voltage-controlled oscillator (VCO), a programmable frequency divider for dividing the frequency of the oscillating signal generated by the VCO by a programmable frequency dividing ratio, a phase comparator for comparing the phase of the frequency-divided oscillating signal with a reference signal of constant frequency and phase, and a feedback loop for feeding back the phase error produced by the phase comparator so as to determine the frequency of the VCO accordingly. As the dividing ratio of the programmable frequency divider changes, the frequency of the frequency-divided oscillating signal supplied to the phase comparator correspondingly changes. This, in turn, results in a change in the fed back error signal so as to modify the frequency of the oscillating signal. The frequency dividing ratio can be established by, for example, a digital code. Therefore, the tuning condition of the tuning section can be determined as a function of this digital code.
The digital code corresponding to a particular broadcasted frequency, or channel, is used as a channel identity code. If a number of these channel identity codes are stored, the tuning section can be tuned rapidly to a predetermined channel merely by reading out the desired code and supplying this code to the programmable frequency divider. This code initially can be derived, or preset, by incrementing or decrementing a digital counter during a so-called set-up operation. The contents of this counter are supplied to the programmable frequency divider so that as this count changes, the tuning condition of the tuning section is swept across the broadcast frequency spectrum. When a desired frequency, or channel, is received, the counter is maintained at its then-existing count, thus establishing the frequency divider ratio of the programmable frequency divider. This count then can be stored in a storage device, or at a particular location in a memory device, which can be addressed for future read out.
While a system of the aforedescribed type may operate satisfactorily to tune the tuning section to particular ones of various predetermined channels, the operating condition of the receiving apparatus in which the tuning section is provided nevertheless may be less than optimum. As is known, in radio receiving apparatus for receiving stereophonic broadcasts of high fidelity, various control elements may be provided in order to adjust the operating conditions of the apparatus for the satisfactory reception of weak signals. Thus, a selectivity control element may be provided for narrowing the frequency band of, for example, the IF stage. This improves the selectivity of the receiving apparatus by limiting the output of the IF stage to a relatively narrow frequency spectrum centered on the desired broadcast frequency which may be adjacent an undesired broadcast frequency. Hence, by narrowing the frequency band, and thus improving the selectivity, interference due to the undesired adjacent broadcast frequency is avoided. Of course, in the absence of an interfering adjacent broadcast frequency, the frequency band of the IF stage preferably is enlarged to a normal range.
Another control element which, preferably, is provided is a mode selecting element. The mode selecting element is operable to change over the operation of the radio receiving apparatus from, for example, a stereo mode to a monaural mode. In the stereo mode, the usual demodulator, which may be a multiplex (MPX) stereo demodulator, is operated to demodulate and combine the usual mono signal (formed of the sum of the left and right channels L+R) and the stereo signal (formed of the difference between the left and right channels L-R) to produce separate channel information. In the mono operating mode, the demodulator merely demodulates the mono (L+R) signal and supplies this demodulated mono signal to each speaker. If the received broadcast signal is relatively weak, the stereo signal, which is modulated onto a higher subcarrier, may be accompanied by undesired interference. Hence, if the demodulator is operated in its stereo mode, the reproduced signals may be less favorable than if the demodulator is operated in its mono mode. The mode control element permits the user of the receiving apparatus to select the particular mode which is most favorable to him.
Yet another control element which may be provided in the radio receiving apparatus is a muting element. Depending upon the strength of the received broadcast signal, as well as the strength of signals which are broadcasted over adjacent frequencies, a more favorable operating condition is attained in some instances when the muting element is operated to permit a muting operation to be performed; while in other instances, a more favorable condition may exist when the muting operation is not performed.
In radio receiving apparatus of the type described hereinabove wherein a storage or memory circuit is provided to store preset channel identity codes, the reading out of a particular channel identity code, although effective to establish a particular tuning condition of the tuning section, has no effect upon the particular selectivity, mode and muting conditions of the receiving apparatus. For example, for optimum reception of the broadcasted program identified as channel 1, the selectivity function should be "narrow", the mode should be "stereo" and the muting operation should be "on". When channel 1 is selected for reception, these conditions may not be present. Thus, the user must operate the aforementioned control elements in order to obtain the optimum receiving conditions. As another example, if the broadcasted program associated with channel 2 is selected, the optimum receiving conditions for this program may be a "wide" selectivity, a mono mode and the muting operation should be "off". In order to provide these conditions, the user must operate the control elements to achieve these individual functions.
Thus, the advantage of so-called "one button" tuning is not attained by the aforedescribed apparatus. That is, although the operation of a single "button" will tune the tuning section to a corresponding preset channel, the operating conditions of the receiving apparatus may not be correct for that channel. Therefore, it is desirable for the user to determine the proper operating conditions of the signal receiving apparatus during the initial, or set-up, operation, whereby control signals representing these proper operating conditions can be stored with the channel identity code. When a particular channel is selected, the preset channel identity code and control signals are read out of the storage device and used to tune the tuning section to the preset channel and also to establish the optimum operating conditions of the receiving apparatus for that channel.